1. Field of the Invention
The present invention relates to pneumatic and hydraulic control systems comprising a number of actautors, and more particularly to methods of synchronizing actuators and apparatus for implementing the same.
Still more particularly, the present invention relates to methods of and apparatus for synchronizing two or more actuators of prime or secondary movers operating in parallel into a common load.
The present invention can most advantageously be used in multiple-unit transport power plants comprising Diesel engines or turbines and providing at the same time the operation of an electric generator.
2. Description of the Prior Art
At present the ships of various types are often equiped with two-unit Diesel power plants where the movers operate into a common load, viz. one propeller. In those cases, when two or more prime or secondary movers operate into a common load it becomes necessary to provide equal load distribution between these units, especially when the load changes. Thus, for example, if the total load on the movers is sharply increased due to external reasons, each of these movers should continue to contribute into the total load, its contribution being equal in magnitude to that prior to the increase. It means that correlation between the contributions of individual movers to the total load should remain unchanged.
Equalization of the load is provided through corresponding synchronization of the operation of the mover actuators, in particular fuel or any other energy supply regulators. The main reasons accounting for unequal load distribution between the engines are the following:
unequal time of response to the change of the load in various movers or, in other words, unequal time constant of the movers;
unequal character of transmission, in actuators of different movers, of a control signal applied to said actuators from the common setting device into useful movement of their operating members due to unavoidable deviations in geometrical dimensions of the elements constituting the actuators as well as due to their temporary misadjustment, etc.;
unequal speed of transmission of control signals both through the common control circuit and through feedback circuits.
Unequal distribution of the load between the movers results in the loss of preset speed or moments and increased fuel consumption as well as underloading or overloading of some movers and thereby their premature ware and even failure. The present invention is directed at providing a method of synchronizing actuators and an apparatus implementing said method ensuring uniform distribution of the common load between the movers.
Known to the art is a method of synchronizing actuators (Cf. USSR Inventor's Certificate No. 496381, published in 1973), applied in control of mechanized tunnel shield. This method comprises the steps of measuring in the process of the tunnel shield operation, the values of displacement of the operating members, namely the rods of all hydrocylinders used therein with respect to a base point, deriving signals corresponding to the displacement of each rod, separating out of said signals the lowest one and separately comparing the obtained signals to derive a correction signal used for adjusting the position of the rod of each hydrocylinder through changing the supply of the pressure fluid to its operating volume, said correction signal being proportional in magnitude to the difference between the signal corresponding to the displacement of the rod of any hydrocylinder and the signal corresponding to the shortest displacement of all the rods relative to the base point.
Synchronization of hydrocylinders in accordance with this method is a complicated process requiring the sequence of the following procedures:
comparing the rod position of each hydrocylinder with the position of the base point;
selecting out of the displacement of the rods of hydrocylinders the shortest displacement;
deriving from several comparing devices control signals proportional in magnitude to disagreement between the position of the rod of each hydrocylinder and the position of the rod of the hydrocylinder deviated by minimum value from the position of the base point.
Such intricate scheme of producing control action fails to provide sufficient accuracy and synchronization speed of the actuators.
The apparatus implementing the afore-mentioned method comprises a setting device adapted to exert a common control action on the movement of the rod of each hydrocylinder, displacement transducers for the rods of hydrocylinders and adjustable pressure fluid sources, each of said sources being connected with one of the hydrocylinders through an individual line accommodating an electrohydraulic regulator. In this apparatus the output of each of the displacement transducer is connected to one of the inputs of a means adapted to derive a signal of minimum error between the position of the base point and the position of each rod of hydrocylinders as well as to one of the inputs of one of the main comparing devices, the other input of each said device being connected to the output of the means of producing said signal, while the output thereof being connected to the control input of one of the electrohydraulic regulators. The output of each displacement transducer is connected, besides, to one of the inputs of one of the additional comparing devices, the other input of each said device being connected to the output of the setting device and its output being connected to one of the pressure fluid sources.
Thus, this apparatus comprises a comparatively large number of elements and therefore it is rather complicated in design. In the above apparatus each hydrocylinder to be synchronized is associated with one pressure fluid source and with two comparing devices, one of which besides is controlled by the auxiliary means adapted to select minimum deviation from the position of the base point. As a result, the reliability and speed of response of this apparatus are comparatively low. Moreover, application and potentialities of this apparatus are limited by the necessity to use the base point.
Also known to the prior art is a method of synchronizing actuators (Cf. U.S. Pat. No. 3,772,884, published Nov. 20, 1973), which actuators are the regulators of the prime movers driving a common load, each having a movable operating device providing fuel supply to the associated prime mover. This method comprises the steps of measuring the movement of the operating device of the regulators, corresponding in magnitude to the fuel supply and therefore the loads on the associated engines to derive signals corresponding to the movement of each operating member of each regulator, comparing said signals to derive a single signal which is the average of said signals followed by separate comparing each said signal corresponding to the movement of each operating member of each regulator against the signal corresponding to the average of said signals, and adjusting the position of the operating member of each regulator in a direction and by an amount proportional to the correction signal derived from said comparison. The correction signal is produced in such a way that it is proportional in magnitude to the difference between the signal corresponding to the movement of the operating member of any one of the regulators and the signal which is the average of movements of the operating member of all the regulators.
The apparatus implementing this method of synchronizing actuators, described in the afore-mentioned U.S. Pat. No. 3,772,884, comprises a setting device adapted to exert a common control action on the movement of the operating member of each regulator, a pressure fluid source associated with transducers of the movement of the operating members of the regulators and with a comparing device adapted to produce a control action on the regulators and associated with the regulators and with the transducers of the movement of the operating members of said regulators. The comparing device is a multichamber adding element having a housing accommodating an axially movable stem and a spring-loaded valve which can be in contact with said stem. Secured to the stem are diaphragms dividing the interior of the housing into positive control chambers providing the movement of the stem in one direction in response to the pressure build up therein and into negative control chambers providing the movement of the stem in the opposite direction. The housing also accommodates an inlet chamber actuating the valve and thereby providing transmission of the control action from the pressure fluid source to the actuators due to the movement of the stem in said one direction by the sum of the pressures in the positive control chambers exceeding the sum of the pressures in negative control chambers, and an outlet chamber communicated with the inlet chamber and operatively associated with the fluid pressure drain means when the sum of the pressures in the negative control chambers exceeds said sum in the positive control chambers. The positive control chambers of the multi-chamber adding element are connected with the transmitters of the movement of the operating member of the regulators and the negative control chambers are connected with each other, their common output being connected through intermediate two-chamber comparing device with the operating member of the regulators. Due to such connection of the negative and positive control chambers a signal is derived which is an average of the movements of said operating members of the regulators. In more details, the common output of the negative control chambers is connected with one of the chambers of each intermediate two-chamber comparing device, the other chamber of which is connected with the transmitter of the movement of the operating member of one of the regulators, the output movable element of this comparing device being connected with the operating member of the same regulator.
In spite of the fact that the afore-mentioned method and the apparatus implementing this method have some advantages as compared to the prior described one they do not still provide sufficiently high accuracy and quickness of synchronization of the actuators and therefore the accuracy and quickness of the process of equalization of the load between the associated prime movers operating in parallel. This is stipulated by the fact that, in the first place, this method and apparatus for implementation thereof comprise two steps of signal comparison, each of said steps introducing its own error into the process of synchronization and, in the second place, in one of these comparing steps a signal is used which is the average of the movement of the operating members. The use of such average value accounts for comparatively low correction signal and results in, in general, still further decrease in the value of the correction signal with the increase in the number of synchronized actuators. Moreover, the use of the average value introduces itself some uncertainty into the process of synchronization. It is necessary also to point out the fact that in the apparatus realizing said method the common control action is transmitted from the setting device to the regulators through an additional means and that the element disconnecting the comparing device from the synchronizing circuit introduced from the purpose of more comfortable manipulation of said apparatus comprises a lot of valve means complicating the construction of this apparatus.